Incorrect mmap behavior about zfs HOT 6 CLOSED

#include <stdio.h>
#include <fcntl.h>
#include <stdlib.h>
#include <sys/mman.h>

int main(int argc, char **argv)
{
    unsigned char buffer[256];
    int i, fd;
    unsigned char *addy = NULL;
    unsigned int off = 0;

    for (i = 0; i < 256; i++)
        buffer[i] = i;

    fd = open("/BOOM/file", O_TRUNC|O_CREAT|O_RDWR, 0644);
    if (fd < 0) exit(1);

    for (i = 0; i < 240808; i+=256)
        write(fd, buffer, 256);

    close(fd);

    fd = open("/BOOM/file", O_RDONLY);
    if (fd<0) exit(2);

    addy = mmap(NULL,240808, PROT_READ, MAP_FILE|MAP_PRIVATE, fd, 0);
    if (addy==MAP_FAILED) {
        perror("mmap");
        exit(3);
    }

    printf("reading with mmap (%p)\n", addy);

    off = 0x2ac30;
    printf("Bytes at offset 0x%04x are:\n", off);

    for (i = 0; i < 16; i++)
        printf("0x%02x ", addy[off+i]);
    printf("\n");

    munmap(addy, fd);
    close(fd);
    return 0;
}

# hexdump -C /BOOM/file|less
0002ac30  30 31 32 33 34 35 36 37  38 39 3a 3b 3c 3d 3e 3f  |0123456789:;<=>?|

# ./map_test 
reading with mmap (0x103ca7000)
Bytes at offset 0x2ac30 are:
0x00 0x01 0x02 0x03 0x04 0x05 0x06 0x07 0x08 0x09 0x0a 0x0b 0x0c 0x0d 0x0e 0x0f 

Jul  2 14:28:36 Lundmans-Mac kernel[0]: +vnop_pagein: off 0 size 32768
Jul  2 14:28:36 Lundmans-Mac kernel[0]: vaddr 0xffffff805bafd000 with upl_off 0
Jul  2 14:28:36 Lundmans-Mac kernel[0]: reading from off 0 into address 0xffffff805bafd000
Jul  2 14:28:36 Lundmans-Mac kernel[0]: reading from off 1000 into address 0xffffff805bafe000
Jul  2 14:28:36 Lundmans-Mac kernel[0]: reading from off 2000 into address 0xffffff805baff000
Jul  2 14:28:36 Lundmans-Mac kernel[0]: reading from off 3000 into address 0xffffff805bb00000
Jul  2 14:28:36 Lundmans-Mac kernel[0]: reading from off 4000 into address 0xffffff805bb01000
Jul  2 14:28:36 Lundmans-Mac kernel[0]: reading from off 5000 into address 0xffffff805bb02000
Jul  2 14:28:36 Lundmans-Mac kernel[0]: reading from off 6000 into address 0xffffff805bb03000
Jul  2 14:28:36 Lundmans-Mac kernel[0]: reading from off 7000 into address 0xffffff805bb04000

Seed set to 1372752561
truncating to largest ever: 0x1497c
data miscompare @ 16880
LOG DUMP (5 total operations):
1: SKIPPED (no operation)
2: SKIPPED (no operation)
3: SKIPPED (no operation)
4: TRUNCATE UP     from 0x0 (0) to 0x1497c (84348)      ******WWWW
5: READ            0x41f0 (16880) thru 0xfc53 (64595)   (0xba64 (47716) bytes) ***RRRR***
data miscompare @ 16880
OFFSET     GOOD       BAD        LENGTH     BADOP#   Last: WRITE    TRUNC-   TRUNC+  
0x0000d000 0x00000000 0x00000006 0x00000830 -1             -1       -1       4  

    ubc_setsize(vp, end);